public class TestArgs3 {
    public static void main(String[] args) {

        int A = Integer.parseInt(args[0]);
        System.out.println(s.sum(A));
    }

    static class s {
        static int sum(int num) {
            int result;
            if (num == 1)
                result = 1;
            else
                result = num + sum(num - 1);
            return
                    result;
        }
    }
}